The actuator of certain emission control valves comprises a solenoid that comprises an electromagnet coil and a stator having an air gap at which magnetic flux acts on an armature. The armature motion is transmitted to a valve element to allow flow through a passageway of the valve. Armature motion is resisted by a return spring that acts on the armature, either directly or via the valve member, to bias the armature to a position that causes the valve element to close the passageway.
The stator air gap is defined by an upper pole piece that is disposed at an upper end of the coil and a lower pole piece at the lower end of the coil. The pole pieces have respective annular hubs that fit into an interior space bounded by the coil, approaching each other from opposite ends of the coil. The juxtaposed ends of the two hubs are spaced apart to define the air gap as an annular space about the armature. Electric current in the coil creates magnetic flux that passes from one hub across the air gap to the armature, through the armature, and back across the air gap to the other hub. The flux causes magnetic force to be applied to the armature, and the axial component of that force acts to displace the armature along the centerline of the solenoid.
In order to operate the valve from closed to open, the solenoid must apply a force that is greater than the bias force being applied by the spring. When a greater spring force is needed for a given valve in a given application, the solenoid must be capable of developing increased force. Because of certain constraints, it may not be possible to simply use a larger, more forceful solenoid. Accordingly, a potentially desirable objective would be to make certain modifications to basic elements of an emission control valve actuator that can increase actuator force without necessarily simply increasing overall size, and inherently weight as well, of the actuator.